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Class: RuboCop::Cop::Style::ZeroLengthPredicate

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::RuboCop::Cop::AutoCorrector, ::RuboCop::Cop::Base, ::RuboCop::ExcludeLimit, NodePattern::Macros, RuboCop::AST::Sexp
Instance Chain:
Inherits: RuboCop::Cop::Base
Defined in: lib/rubocop/cop/style/zero_length_predicate.rb

Overview

Checks for numeric comparisons that can be replaced by a predicate method, such as receiver.length == 0, receiver.length > 0, and receiver.length != 0, receiver.length < 1 and receiver.size == 0 that can be replaced by receiver.empty? and !receiver.empty?.

Note
File, Tempfile, and StringIO do not have empty? so allow size == 0 and size.zero?.

Examples:

# bad
[1, 2, 3].length == 0
0 == "foobar".length
array.length < 1
{a: 1, b: 2}.length != 0
string.length > 0
hash.size > 0

# good
[1, 2, 3].empty?
"foobar".empty?
array.empty?
!{a: 1, b: 2}.empty?
!string.empty?
!hash.empty?

Cop Safety Information:

  • This cop is unsafe because it cannot be guaranteed that the receiver has an empty? method that is defined in terms of length. If there is a non-standard class that redefines length or empty?, the cop may register a false positive.

Constant Summary

::RuboCop::Cop::Base - Inherited

EMPTY_OFFENSES, RESTRICT_ON_SEND

Class Attribute Summary

::RuboCop::Cop::AutoCorrector - Extended

::RuboCop::Cop::Base - Inherited

.gem_requirements, .lint?,
.support_autocorrect?

Returns if class supports autocorrect.

.support_multiple_source?

Override if your cop should be called repeatedly for multiple investigations Between calls to on_new_investigation and on_investigation_end, the result of processed_source will remain constant.

Class Method Summary

::RuboCop::Cop::Base - Inherited

.autocorrect_incompatible_with

List of cops that should not try to autocorrect at the same time as this cop.

.badge

Naming.

.callbacks_needed, .cop_name, .department,
.documentation_url

Returns an url to view this cops documentation online.

.exclude_from_registry

Call for abstract Cop classes.

.inherited,
.joining_forces

Override and return the Force class(es) you need to join.

.match?

Returns true if the cop name or the cop namespace matches any of the given names.

.new,
.requires_gem

Register a version requirement for the given gem name.

.restrict_on_send

::RuboCop::ExcludeLimit - Extended

exclude_limit

Sets up a configuration option to have an exclude limit tracked.

transform

Instance Attribute Summary

Instance Method Summary

::RuboCop::Cop::Base - Inherited

#add_global_offense

Adds an offense that has no particular location.

#add_offense

Adds an offense on the specified range (or node with an expression) Unless that offense is disabled for this range, a corrector will be yielded to provide the cop the opportunity to autocorrect the offense.

#begin_investigation

Called before any investigation.

#callbacks_needed,
#cop_config

Configuration Helpers.

#cop_name, #excluded_file?,
#external_dependency_checksum

This method should be overridden when a cop’s behavior depends on state that lives outside of these locations:

#inspect
#message

Gets called if no message is specified when calling add_offense or add_global_offense Cops are discouraged to override this; instead pass your message directly.

#name

Alias for Base#cop_name.

#offenses,
#on_investigation_end

Called after all on_…​

#on_new_investigation

Called before all on_…​

#on_other_file

Called instead of all on_…​

#parse

There should be very limited reasons for a Cop to do it’s own parsing.

#parser_engine,
#ready

Called between investigations.

#relevant_file?, #target_rails_version, #target_ruby_version, #annotate, #apply_correction, #attempt_correction,
#callback_argument

Reserved for Cop::Cop.

#complete_investigation

Called to complete an investigation.

#correct, #current_corrector,
#current_offense_locations

Reserved for Commissioner:

#current_offenses, #currently_disabled_lines, #custom_severity, #default_severity, #disable_uncorrectable, #enabled_line?, #file_name_matches_any?, #find_message, #find_severity, #range_for_original, #range_from_node_or_range,
#reset_investigation

Actually private methods.

#use_corrector

::RuboCop::Cop::AutocorrectLogic - Included

::RuboCop::Cop::IgnoredNode - Included

Constructor Details

This class inherits a constructor from RuboCop::Cop::Base

Instance Method Details

#check_nonzero_length_comparison(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 81

def check_nonzero_length_comparison(node)
  nonzero_length_comparison = nonzero_length_comparison(node.parent)
  return unless nonzero_length_comparison

  lhs, opr, rhs = nonzero_length_comparison

  return if non_polymorphic_collection?(node.parent)

  add_offense(
    node.parent, message: format(NONZERO_MSG, current: "#{lhs} #{opr} #{rhs}")
  ) do |corrector|
    corrector.replace(node.parent, replacement(node.parent))
  end
end

#check_zero_length_comparison(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 66

def check_zero_length_comparison(node)
  zero_length_comparison = zero_length_comparison(node.parent)
  return unless zero_length_comparison

  lhs, opr, rhs = zero_length_comparison

  return if non_polymorphic_collection?(node.parent)

  add_offense(
    node.parent, message: format(ZERO_MSG, current: "#{lhs} #{opr} #{rhs}")
  ) do |corrector|
    corrector.replace(node.parent, replacement(node.parent))
  end
end

#check_zero_length_predicate(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 54

def check_zero_length_predicate(node)
  return unless zero_length_predicate?(node.parent)
  return if non_polymorphic_collection?(node.parent)

  offense = node.loc.selector.join(node.parent.source_range.end)
  message = format(ZERO_MSG, current: offense.source)

  add_offense(offense, message: message) do |corrector|
    corrector.replace(offense, 'empty?')
  end
end

#non_polymorphic_collection?(node) (private)

Some collection like objects in the Ruby standard library implement #size, but not #empty. We ignore those to reduce false positives.

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 143

def_node_matcher :non_polymorphic_collection?, <<~PATTERN
  {(send (send (send (const {nil? cbase} :File) :stat _) ...) ...)
   (send (send (send (const {nil? cbase} {:File :Tempfile :StringIO}) {:new :open} ...) ...) ...)}
PATTERN

#nonzero_length_comparison(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 110

def_node_matcher :nonzero_length_comparison, <<~PATTERN
  {(call (call (...) ${:length :size}) ${:> :!=} (int $0))
   (call (int $0) ${:< :!=} (call (...) ${:length :size}))}
PATTERN

#on_csend(node)

Alias for #on_send.

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 50

alias on_csend on_send

#on_send(node) Also known as: #on_csend

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 45

def on_send(node)
  check_zero_length_predicate(node)
  check_zero_length_comparison(node)
  check_nonzero_length_comparison(node)
end

#other_length_node(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 134

def_node_matcher :other_length_node, <<~PATTERN
  {(call $(call _ _) _ _)
   (call _ _ $(call _ _))}
PATTERN

#replacement(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 115

def replacement(node)
  length_node = zero_length_node(node)
  if length_node&.receiver
    return "#{length_node.receiver.source}#{length_node.loc.dot.source}empty?"
  end

  other_length_node = other_length_node(node)
  "!#{other_length_node.receiver.source}#{other_length_node.loc.dot.source}empty?"
end

#zero_length_comparison(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 102

def_node_matcher :zero_length_comparison, <<~PATTERN
  {(call (call (...) ${:length :size}) $:== (int $0))
   (call (int $0) $:== (call (...) ${:length :size}))
   (call (call (...) ${:length :size}) $:<  (int $1))
   (call (int $1) $:> (call (...) ${:length :size}))}
PATTERN

#zero_length_node(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 126

def_node_matcher :zero_length_node, <<~PATTERN
  {(send $(call _ _) :== (int 0))
   (send (int 0) :== $(call _ _))
   (send $(call _ _) :<  (int 1))
   (send (int 1) :> $(call _ _))}
PATTERN

#zero_length_predicate?(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/zero_length_predicate.rb', line 97

def_node_matcher :zero_length_predicate?, <<~PATTERN
  (call (call (...) {:length :size}) :zero?)
PATTERN